Pentostatin is (R)-3-(2-deoxy-.beta.-D-erythropentofuranosyl) -3,6,7,8-tetrahydroimidazo [4,5-d]-[1,3]diazepin-8-ol having the structure: ##STR1## It is a potent adenosine deaminase inhibitor and is useful as an antileukemic agent. U.S. Pat. No. 3,923,785, issued Dec. 2, 1975, describes the production of pentostatin by fermentation of a strain of Streptomyces antibioticus which is on deposit as NRRL 3238. U.S. Pat. No. 3,923,785 also describes the isolation and purification of pentostatin from the fermentation beer.
The present invention provides a markedly improved procedure for the isolation and purification of pentostatin. The present invention utilizes a combination of ion exchange resins and SEPABEADS 207 which has proven to increase dramatically the amount of pure compound recovered from the fermentation broth. Without this improved recovery process the commercialization of pentostatin would be impractical due to the high cost of production of the compound in pure form.